(1) Field of the Invention
The present invention relates generally to a process for extracting and refining soybean oil and to the resultant product, and in particular to an improved method of separating soybean oil that is high in calcium and/or magnesium, permitting physical refining of the oil.
(2) Description of the Prior Art
Soybean oil production involves several steps that are necessary to render the soybean oil suitable for human consumption. These production steps may be broadly characterized as 1) soybean preparation, 2) oil extraction, and 3) oil refining. Soybean preparation generally includes the steps of cleaning, drying, cracking, and dehulling.
The great majority of commercial soybean oil production processes extract or separate the oil from the soybean meal by a process known as solvent extraction. In the solvent extraction process, the prepared beans are first flaked to provide a large surface area. A solvent, commonly hexane, is then pumped through the soybean flakes to dissolve the oil in the hexane, separating approximately 99.5% of the oil from the meal. The hexane is then separated from the oil and recycled.
The crude oil resulting from the solvent extraction must then be subjected to additional treatments, collectively called “refining”, to remove various materials in order for the oil to be suitable for consumption. These materials include hydratable and non-hydratable phospholipids, free fatty acids, and various color and flavor components. Crude soybean oil contains phosphorous compounds called hydratable phospholipids, and small amounts of calcium and magnesium that complex with a portion of the phospholipids to form non-hydratable phospholipids. Hydratable phospholipids are normally removed by a process known as “degumming”, in which the oil is agitated or otherwise intimately combined with water to precipitate gums from the oil. The gums are then removed by centrifuging.
These precipitated gums can be used as a feed additive, or evaporated to remove moisture. The end product, lecithin, has various end uses such as food emulsifier. The degummed oil is dried under vacuum to remove any water. Removal of non-hydratable phospholipids is considerably more difficult and expensive, requiring further chemical treatment, typically chemical refining, to break the chemical bonds between the calcium or magnesium ions and the phospholipids, followed with extensive bleaching of the oil.
In most processes, free fatty acids are removed from the oil by a process known as caustic refining, also called chemical or alkali refining, in which the oil is mixed with a caustic material, such as sodium or potassium hydroxide, which undergoes a saponification reaction with the acids, forming soaps that are then removed by centrifugation. Non-hydratable phospholipids are removed along with the free fatty acids. Chemical refining soybean oil is an expensive process, requiring a large investment in capital equipment. In addition, a significant quantity of the oil is captured by the soaps, adversely affecting oil yield. Also, the caustic refining process produces soapstock, which has little commercial value, and it is difficult to dispose of without environmental problems.
Conventional refining processes also involve some bleaching of the soybean oil to remove color pigments that adversely affect the color of the oil. Finally, chemicals that add flavors to the oil are removed by a process known as “deodorization”, which is essentially a form of physical distilling, in which the oil is subjected to high temperatures under a vacuum for a short period of time, which is sufficient to remove the flavor-causing components, but insufficient to break down non-hydratable phospholipids.
Commonly assigned U.S. Pat. No. 6,511,690, issued Jan. 28, 2003, and copending U.S. patent application Ser. No. 10/066,250, filed Jan. 31, 2002, both the patent and application being incorporated herein by reference in their entirety, describe an alternative process for producing soybean oil having a commercially acceptable frylife, i.e., at least 30 fry cycles, without partial hydrogenation by a combination of mechanical oil extraction combined with physical refining of the crude oil. In the process described therein, soybean oil is mechanically separated from prepared soybeans by first rapidly heating the beans for up to about 60 seconds to a temperature of from about 300° F. to about 370° F., preferably from about 315° F. to about 335° F., followed by mechanically pressing the oil from the beans. Desirably, the beans are crushed during or after heating to assist in freeing the oil, e.g., by extruding the beans through an extruder in which the beans are subjected to high pressures that crush the beans while frictionally heating the beans.
The crude soybean oil is then degummed by intimately mixing the crude soybean oil with water, which may contain citric acid or a similar organic acid, to form gums of the hydratable phospholipids, which are then removed from the crude oil, e.g., by centrifuging. The degummed oil is then bleached with bleaching materials, such as clay or silica gel. The oil is then vacuum dried and filtered.
The resultant oil is a useful product known as refined and bleached oil. Normally, however the oil is further processed to remove free fatty acids and components that contribute to the color and flavor of the oil. Free fatty acids are then removed along with undesirable flavor and color components by physical refining, in which the oil is heated in a distillation column to from about 450° F. to about 500° F. to distill off the free fatty acids and flavor materials.
While the combination of mechanical extraction with physical refining results in several improvements over the solvent extraction and caustic refining process, use of physical refining is not possible for soybean oil containing a high amount of magnesium and calcium salts, i.e., more that 100 ppm. Therefore, further improvements are still needed in order to permit refining of soybean oils that are unusually high in calcium and magnesium.